U.S. Pat. No. 6,303,149 describes a process for preparing sol-gel microcapsules loaded with functional molecules by emulsifying sol-gel precursors and the functional molecules in an aqueous solution, and mixing the emulsion with an acidic, neutral or basic aqueous solution to obtain a suspension of microcapsules.
EP-A-941761 describes a process for preparing microcapsules with an organopolysiloxane shell and a core material, in which the shell is formed in situ by hydrolysis and polycondensation of an organosilane and/or a condensation product thereof having at most 4 silicon atoms.
WO-A-03/066209 discloses a process for encapsulating a lipophilic cosmetic, chemical, biological or pharmaceutical active material composition, in which a water reactive silicon compound comprising tetraalkoxysilane is added to an aqueous emulsion of the active material composition having a positive zeta-potential, whereby the tetraalkoxysilane condenses and polymerises at the interface of the emulsified droplets of the lipophilic active material composition to form microcapsules having a core of the active material composition surrounded by a shell of silicon-based network polymer.
WO-A-2008/002637 discloses a process for preparing microcapsules by mixing an oil phase and an aqueous solution of a cationic surfactant to form an oil in water emulsion, and adding a water reactive silicon compound comprising tetraalkoxysilane to the emulsion so that the tetraalkoxysilane condenses and polymerises at the oil/water interface as described above. The amount of cationic surfactant is 0.1% to 0.3% by weight based on the oil phase and the shell thickness of the microcapsules is at least 18 nm.
The above prior patent applications relate mainly to encapsulation of sunscreens. Since sunscreens are effective in screening UV rays even when encapsulated, it is preferred that the rate of diffusion or leaching from the microcapsules is as low as possible when encapsulating sunscreen. Other active materials, however, may be ineffective if they are encapsulated with no diffusion or leaching from the microcapsules. The objective of encapsulation in this case is to achieve controlled diffusion or leaching from the microcapsules resulting in controlled release or prolonged release of the active material.
Examples of active materials for which controlled release is desired include additives for conditioning substrates like fabric, skin, hair and/or fibres, for example fabric softeners and hair conditioners. There is a demand for a conditioning composition that can be incorporated in a liquid cleaning product so that washing and conditioning can be carried out in a single process. However there is a risk that the conditioner is washed off the fabric or fibre by the cleaning product, particularly in a liquid laundry detergent. Lipophilic skin conditioners are prone to solubilisation in the surfactant-rich base of typical skin and hair cleaning compositions. The solubilised species are generally washed away and do not deposit on the skin or hair.
Examples of active materials for which prolonged release is desired include compositions which impart hydrophobicity, softness and flame retardant properties to textiles, particularly for the treatment of industrial textiles intended for uses such as mattress coverage, curtains, protective clothing, or tenting.